Project: Switch
by Asriel universe
Summary: Due to an experiment gone wrong, Sans and blueberry are in each others timeline! but if they dont find a way back they will be trapped forever in each others timeline forever with no way back
1. Chapter 1

(Sans P.O.V) Sans knew it had to work this time. Once and for all this timeline will be purged of this demon child. He checked his cameras from his lab basement. The child is leaving the ruins! He had to get down there. He teleport's down the forest and greets them way he normally does. Whoopee cushion in the hand trick, then the lamp. He noticed they didn't do behind the lamp this time. He checked their LV. 3, they already have 3 LV. He cursed under his breath. They had initiated a Genocide route this past reset. This meant he had to hurry.

All throughout the forest his suspicions were confirmed, the kid was killing off every monster they came across. Finally they came across the bridge, where Pap's had his machine set up. Once again, the machine didn't activate and the kid continued on their way into snowdin. Before they did they stopped by him "heya kid, if you keep going the way you're going, y o u ' e"

He teleported out of the forest and back into his basement, where he continued to re-program systems and change functions. He looked up at his camera. The kid was just out of the shop, and heading down out of the town. He knew where they were going. To meet Papyrus for their battle. He didn't want to watch but it was like he couldn't look away from the screen.

Papyrus, like so many times before, gave his speech about believing the human could still be good. Sans watched as the Human moved forward once more and the battle initiated. He could see the look on their face. This wasn't just out of curiosity anymore. Sans remembers the first time they initiated a Genocide route. The look on their face was indecisive, as if they weren't sure what to do, but now he could see the look in their eye. They were now just doing this for fun, for the pleasure of it. It was sick and it sickened him almost to the point he wanted to break his promise before he was supposed to, but if this worked, then he wouldn't have to worry about that.

He watched with baited breath, as the human pulled back their fist, the pink-leather glove, wrapped around their hand. He watched as they swung toward Papyrus, and instantly destroyed his body. Pap's head fell to the ground. "W-W-Well, that's not what I-I-I expected, but I still believe in you, you can do better, I know you can!, you just have to try again" and with those famous last words, Papyrus's head disappeared along with the rest of his body.

He came out of his basement and walked down to where it happened. His dust was resting in the ground, almost as if the dust just came out of nowhere, but Sans knew better. Papyrus's scarf was stuck under a clump of snow and was peaceful looking, as if Papyrus had dropped it because he didn't tie it right, and was just looking for it around Snowdin. Sans would find it and take it to him. Pap's would thank him, give him a huge hug, and the pair would go into the forest for sentry duty. Sans scooped up the dust and put it on his scarf, wrapping it up like a bindle, and carried it into the house. He took out the left over spaghetti that papyrus had made last night. Sans was so proud of him, because for once, it had flavor, and texture and was more than frozen noodles with ketchup. Papyrus was bragging about how it was his best one yet, and it was, so it should be savored for as long as possible. Sans scooped out some dust, and warmed up some of the spaghetti. He then took the dust and sprinkled some over the spaghetti. He chuckled because it just looked like he was putting on Parmesan, not the remains of his dead brother. He smiled at the thought of how Papyrus _loathed_ Parmesan cheese. He would always sprinkle some on his plate whenever it was made, sometimes just to spite Papyrus, and because he liked it. Papyrus would get mad and say something like "Sans!, don't do that!, it ruins the flavor of the Spaghetti!". Sans would chuckle and try a bite with the cheese on it and say "Heh you're right bro, I don't think I can eat this, seeing as it made such a _cheesy_ gesture at me". Papyrus would scold him for the pun, and for putting Parmesan, but would laugh and sit down to eat anyways.

He took the plate of spaghetti and put it on top of the fridge. It didn't matter, everything would reset eventually. He went back down to the basement, and checked his cameras. The kid had already made it past Gerson's shop and was in the hallway of echo flowers. He had to hurry. He continued to work and watch the kid the same time. They walk past Temmie village where the room goes dark and they encounter Undyne, only for the Monster kid, to once again, get in the way and be carted off.

Sans watched as they went up to the bridge, and the Monster Kid called out to them. Sans watched the humans face carefully. Every single time, whenever the Human fought Monster Kid, the look on their face was always sorrow and regret, but this time the human didn't even hesitate as they rushed forward and stuck out their foot, ready to land a blow to his face, and always at the last second, Undyne would get in the way, and Monster Kid would leave. Every time, he would watch in amazement as Undyne transformed, while speaking to the human with such a powerful voice that even he felt inspired to go and help her, but sadly, he couldn't interfere.

7 times. That is how many times he felt time go back a little. He caught himself repeating actions, or recounting swears he took the same drink of coffee every couple of minutes. He watched as the human initiated the Undyne fight once more, and started to deliver killing blows. He watched as Undyne just took each attack like it was nothing, but Sans wasn't stupid. He knew, that even though Undyne had high stats in this form, that no one was invincible.

He watched as The human delivered the killing blow, and Undyne stood shaken. "d-d-damn it!, not even that power was enough?...well, if y-y-you think that im gonna give up, you're wrong! I've got my f-f-friends behind me. Alphys said she would watch me fight you, and i-i-if anything went wrong, she would e-e-e-vacuate everyone!, by now, she has already called Asgore, and told him to absorb the six human souls". Undyne was melting now. "a-a-and with that kind of power, THIS WORLD WILL LIVE ON!" She was smiling her biggest smile, even as she was dying, because she knew that even though she had lost the battle, the war was far from over.

Sans watched carefully as they made their way into Hotland. He saw them talk with Mettaton and continue out into the next area. They walked all through Hotland and finally made it to Mettaton. He watched, as he's done a thousand times before, as Mettaton transformed into his original form. He watched, helplessly, as they pulled out their gun, and fired six shots in quick succession. The lights faded out and Mettaton was shaking. "S-s-s-o, I gu-gu-guess you don't want to join my f-f-fan club?" and with those last words, an explosion rocked the area. He watched as the human continued down their path. He had to hurry, because at this rate the human would be at the judgement hall before he could finish. He watched as they found their way through Asgores home, and unlatched the key, all while the weed was telling them the story of how he died.

It was done, he had finished it. He looked up at his camera. His stomach turned into knots. they were at the Judgment hall, walking through it, about to stop and be prepared to greet him. He had to get down there now or the kid would reset and he would have lost so much progress. He teleports in at the last second.

"Heya, I see you've been busy. So, can I ask you a question?" He went through with the normal mantra. "Do you believe that even the worst person can change?", that anyone can be good if they just try?, heheheheheh, Ive got another question for you" He said. "Do you wanna have a bad time?, because if you take another step forward, you're really not gonna like what happens next"

They step forward, as they always do. "whelp, sorry old lady, this is why I don't make promises". He saw the world go dark around him as the battle was initiated. He picked them up, slammed them into the ground and went through the battle as normal.

12 times. This was how many times he had killed them. He knew it in his gut they were getting close. It was this one for sure, that they would land a hit. He watched as the human managed to dodge his ring of Gaster blasters. He saw waiting patiently, as they knew he would fall asleep, he tried his best, but years of laziness had that affect on him. He fell asleep. He managed to dodge the first strike, but since his turn ended they got another strike, and it landed perfectly. He got up. "huh, guess that's it then, whelp, I'm going to grillbys. Papyrus?, do you want anything?"

He stumbled out of the hall and teleported back to his basement. He was running out time, any second now he would be turned to dust. If this worked the world would reset, but the Human wont reset with it. He typed in the remaining variables and activated it. He felt himself being reduced to dust as the world around him was filled with a blinding bright light.


	2. Opposite world

"Where am I?" Blueberry Sans, also known as Underswap Sans, said. He rubbed his eyes, and found that he was in a basement, infront if a machine. Blueberry found the exit, and went upstairs, but not without noticing the dust on the ground first. He looked in the kitchen of the house he was in. He found a plate of spaghetti...

 _ **Sprinkled with monster dust.**_

Blueberry gagged, and ran out of the house, into Snowdin. Had he not gone anywhere after all? Where was Papyrus? He saw a place named, "Grillby's". _Since when did Grillby have a restaurant in Snowdin?_ Blueberry thought. He peeked in the window, and Grillby was in a suit. As a bartender. Only then, he realized... Something's very wrong.

(Sans p.o.v.)

Sans woke up in his bedroom, only, it didn't look like his bedroom at all. It still looked the same, but there were posters of Alphys? on the wall? At least he thought it was Alphys. The person he was seeing had a scar down her left eye, and in other pictures she had an eye patch on it. He looks at his clothing. He still has on his Jacket and shorts, but curiously, he went into his closet. He had some clothes, and _one clean suit of armor_. What was that doing there? He needed to find out where he was and quick! Something was very wrong.

He comes out of his bedroom, and thank goodness the house still looks the same. He comes down the stairs and steps out into Snowdin. He walks around and can see Grillbys from a distance. He sighed in relief. Maybe nothing too bad had happened to the timeline after all. He gets closer and can see that this place _is not Grillbys_. The restaurant still looks the same, but the sign reads _Muffets_ instead. He narrowed his eyes in suspicion and walked in. He goes and sits down on his stool and the first thing he notices is the bartender is indeed Muffet, and not Grillby. Muffet looks at him questioningly. "Sans?, what are you doing in here?, If you're looking for Papyrus he is on sentry duty already, heh, I'm surprised you weren't there first" Muffet said. Sans was and confused "What do you mean?" He asked her. Muffet looked at him again. "Papyrus is already in the forest" she told him.

"Oh ok" he said. He walked out of the bar, and walked into the forest. He kept walking all the way until he could see the door to the ruins. He was about to cross the bridge when someone greeted him. "Hey bro, I see you decided to sleep in today, I'm surprised, you're normally reporting for work in the early hours of the morning" said a voice behind him. Sans turned around "Oh and you're finally sporting the casual look eh?" said Papyrus, only he didn't look like Papyrus. He was in athletic shorts like Sans was, and was wearing an orange pull-over, with a cigarette poking out of his mouth. They both took one good look at each other and recoiled in shock.

"You're-'re-'re _not_ my brother!" they both exclaimed at the same time. Papyrus reacted faster than Sans could and reached out, grabbing him by his soul and lifting him into the air. Sans retaliated by summoning a Gaster blast and firing it at Papyrus. He teleports out of the way but ends up dropping Sans.

Both face each other and charge up a Gaster blaster, but at the last second realize, maybe this _is_ my brother, just a different version? He didn't completely understand, but was sure he would figure out. Sans was the first to lower his weapon. His Gaster blaster disappeared but Papyrus still remained adamant, as if waiting for a reason to blast him. Sans stuck his hands up surrender and told him "Listen, I understand this looks weird, trust me this looks weird to me as well..." He went on to explain what had happened with his timeline and how he ended wherever he was. Papyrus spoke" So, if you're here, then where is my brother, _my sans,_ at?"

Sans shrugged "maybe he ended up in my timeline...?". Papyrus diminished his Gaster blaster. "Listen to me, there is a human going to come out of that door any minute now, and they're going to see something is wrong, and might do something we don't want them to do, So, since in a way you are my brother, you need to act the way my brother does here" Sans looked confused. "and...how does he act here?" he asked. "well in your timeline, you're the lazy one right?, and you're the one who always meets them in the hall of judgement?" Papyrus asked. Sans looked at him. "so you're saying the Sans here acts like my brother?". "I guess, what am I like where you live?" Papyrus asked

"well, you're ambitious, and obsessed with capturing a human in order to join the royal guard, you love to cook, and your hate for puns in unparalleled, but you love it when I make them anyways, your sweet and innocent, but at the same time you're bold and confident" Sans said. Papyrus looked sad. "heh, sounds almost like my brother" He said. "Listen we need to go back to the house" Papyrus teleported them back into Sans room. He went into his closet and took out the suit of armor. "You need to put this on" Papyrus told him. Sans changed as quickly as possible. "alright how do I look?" he asked. "Perfect copy, No one could tell you apart, except for me of course, Now can you do an impression?". "Hmm" Sans pondered "NYEHEHEHE, It is I, the Great Sans!". "Hmm, close" said Papyrus "but my brother says 'mwuehehe' and calls himself the magnificent Sans, try again, and quickly". "Alright" Sans said "MWUHEHEH, IT IS I, THE MAGNIFICENT SANS!" He exclaimed. He looked at Papyrus. He chuckled "Right on the money bro, now lets go greet the human"

Papyrus teleports them back to the forest. "Stay here and wait for my signal" He moves on ahead and pretty soon Sans can see the Human coming down the path, only they don't look like frisk...it hit him, they look like Chara!, but Papyrus didn't seem fazed by this. Chara and frisk must have swapped places in this timeline. "Quick!, behind this conveniently shaped plant!, only Chara didn't move. uh oh. Sans comes out and does what his brother does whenever the human doesn't go behind the lamp. "Hey Papyrus have you found a human yet? "Yeah bro, s'right there" He said. Sans took a quick peek at there stats. 3. 3 LV already. He cursed again under his breath and said "well, I guess that settles it then!" and walked off into the next area.

Papyrus teleported next to him. "Did you see their stats?" Sans asked him. "Yeah, 3 LV already, and they didn't even go behind the plant" Sans started laughing "What's so funny?" Papyrus asked "Sorry, I know this is quite the situation we're in, but I couldn't stop thinking about how in my timeline how it's a lamp, instead of a plant" Sans said "it's like this place is a big opposite world of my timeline, did I see posters of Alphys up on the wall in my room?" He asked. "Yep" said Papyrus "She's the captain of the royal guard, hmm, If Alphys is the captain here, does that make Undyne captain of the Royal guard in your timeline?, and Alphys the royal scientist?" He asked. "Sure does, I guess, I mean, you're right, Undyne is royal guard leader and Alphys is the royal scientist" He said. "Papyrus looked on in alarm and Sans did the same, as the human was moving into the area they were in.


	3. Chapter 3

Blueberry Sans decided that he would go to Undyne's lab. But... When he got there, Alphys opened up. "S-Sans? You look d-different today..." Alphys said. "YOU look different" Blueberry Sans responded. "I always look like this... W-wait a minute... Come in." Alphys said, moving out of the way of Blueberry so that he could step in. He did so. "I'm... Really confused. First, Grillby has a restaurant now, You're not a warrior, and I have a basement in my house!" Blueberry said. "Oh no... You s-see, you really c-come from another universe, a-and the Sans that was h-here must've gotten swapped with you... O-oh boy..." Alphys tried to find the correct sentence structure, but failed. "I...what? So, what i'm getting from this, is that there's another me, and another universe, and I'm from said place." Blueberry said. "T-That's the most basic form..." Alphys said. "Well, how can I get back?" Blueberry asked. "I... Don't know..." Alphys answered. "WHAT DO YOU MEAN YOU DON'T KNOW?!" Blueberry yelled. "I-I... Have to go do something." Alphys said. She walked to the bathroom.

~~Undertale Sans' P.O.V~~

Sans and Papyrus had made it back, and apparently It would be awhile before the Human decided to do anything. Papyrus suggested they visit Undyne, and figure out what is going on. They teleported to the lab, and Papyrus knocked on the door. Undyne opened up and smiled at Papyrus. "Hi-i-i Papyrus, what an unexpected visit, and Sans!, you look quite d-d-d-different today" She stuttered. Sans had changed out of the armor and back into normal clothing. "well, that's because, I'm not the Sans you know" He told her. "w-w-w-w-what do you mean?" She asked. Papyrus spoke up "I think he is from an alternate timeline, where everyone has swapped places, and our Sans, has ended up in that one, while this Sans, has ended up here, basically in his timeline, I take on the role of our Sans, and I am obsessed with capturing a human, and entering the royal guard, while Sans, is the lazy, laid back guy" He explained.

"C-C-Come inside" she said. Undyne led them inside and pulled Sans up to a machine with a head brace. "T-T-This will allow me to analyze your memories, not that I don't believe you, but I want to see for myself". She turned on the machine and the screen came to life. It showed Sans waking up the previous reset before he ended up here. He starts working on the machine, and he teleports down to the forest, and the trio watch as Papyrus does his thing. They watch as Sans watches his brother be murdered, and then, when the human confronted monster kid, Papyrus and Undyne watched in shock as the other Undyne got in the way and take the blow.

They watched as Undyne spoke to the human, and reformed more powerful than ever. Undyne watched with pure admiration on her face, as she knew she would never be able to do that. The trio watched as the human made their way through the core, and slice through Mettaton Neo like butter. They watched as Sans confronted the human, and Sans felt it when he watched as the kids attack hit. He felt the blood running down his chest as the three watched him enter in the remaining variables for the machine. They watched all the way until they saw Undyne hook him up to the machine again.

When it was over, Undyne came up and enveloped him in a hug "I'm sorry" she said "I'm sorry you had to live with this" she told him. Sans hugged back, the whites of his eyes having disappeared. He silently started crying, as he knew, he would probably never be able to see anyone from his universe ever again. Papyrus watched on, secretly hoping it was him, so he wouldn't have watch his brother go through this. Although this version of Sans wasn't Papyrus's brother, he still considered him one.

(Blueberry Sans)

Blueberry listened in confusion as he heard an elevator noise from the "bathroom". _Strange._ He thought. He went upstairs, and was bombarded with a display of anime posters. "Reminds me of Undyne..." Blueberry muttered. As if on cue, the door to the lab opened. "ALPHYS! ARE YOU HEEEEEEERE?" A voice called out. Blueberry peeked out the side of the room. He saw a girl with a red ponytail, blue skin... _Undyne?!_ Blueberry thought. He quickly dashed into a secret door. Blueberry heard Alphys. "O-Oh! Hello Undyne!" She said. "I came to tell you... There's a Mew Mew Kissy Cutie 3." Undyne said. "R-Really?!" Alphys asked. "Really." Undyne answered. "Wow..." Alphys said. "Well, I've gotta go now. Bye Al!" Undyne said. A moment or two later, the sound of the door to the lab opening and closing echoed. "Ok, Sans, you can come out now." Alphys said, coming upstairs. "How'd you know I was hiding?" Blueberry asked. "You didn't come down, so I assumed. Anyway, tonight, you're going to have to sleep here at the lab." Alphys answered, suprisingly not stuttering at all.

[That night...]

Blueberry came out of his hiding spot, double checked if Alphys was truly asleep, and went to the so-called "Bathroom". It turns out it was actually a elevator. "B1?" Blueberry wondered out loud. The elevator started dropping quickly. It hit the ground with a loud thud. "What the heck just happened?!" Blueberry asked no one in particular. He tried to get the elevator to take him back up, but the power was out. "Awww..." Blueberry sighed. He decided to start exploring the new area. He eventually came to 3 sinks. He wondered if all three of them worked, so he turned all three of them on. Out of the third one came some kind of white goop. "Wh-what is that?!" Blueberry wondered. The goop turned into some kind of _really_ screwed up monster. "WHAT IS THAT?!" Blueberry was scared now. The creature made noises. Blueberry was too scared to move.

(Props to a good friend of mine for co-writing this with me)


	4. How to Fix This

~Undertale Sans P.O.V.~

Sans sat there, overwhelmed by the fact that Undyne of all people was the one comforting him. Even back home, where Alphys is the shy, nerdy scientist, she doesn't really seem one to comfort anyone. Maybe this timeline is more than just swapped roles. He hugged back, his eyesockets still darked out. Undyne pulls away, and turns to Papyrus. "How do we fix this?" She asks him. "Hmm, Sans, do you think we could build a version of the machine you used to come here? we could use it to send you home" Papyrus told him. "No, all my blueprints and schematics are back in my timeline" he said.

"damn". "Why don't you two go home and rest, and i'll think of something" Undyne decides to tell them. "Just be careful, ok?" Sans tells her "There is a kid just like the one from my memories on the loose. I don't want to see anyone hurt" "O-o-o-o-ok sans. I will be. I promise" she says. Sans and Papyrus head home for the night. When they get home, Papyrus heads up to his room, and Sans to his.

'Just glad i'm not _sans_ a room at the moment' he thinks to himself. He hops into bed, not bothering to change. Then it hits him. if Papyrus takes his role in the judgement hall. does that mean he has to meet the kid outside of Snowdin tomorrow? He decided if he does, he won't go down as easy as they're used to. He will find a way to live. For his brother, and everyone else counting on him

~That Morning~

Sans wakes up, and stumbles downstairs, and sits at the table, not quite awake yet. Papyrus walks down the stairs, and fixes up some cold Tacos, and places a plate in front of Sans. He opens one eye, and gives it a questioning grunt. He then shrugs his shoulders, and eats it anyways. "It's nice to have something other than spaghetti for breakfast" he says. Papyrus looks at him and says, "oh, so that's my cooking passion. I've been wondering" "heh, yeah" Sans tells Papyrus about all the times his Papyrus made spaghetti.

Then Papyrus gets serious. "Are you ready? to meet the human?" He asks. "Yeah, I have a plan. i'm not going down without a fight. and in the end the kid will believe i'm dead" Sans said. "Believe?" Papyrus asked "oh, I see what you're playing at" He said. "hmmh" He finishes his Taco. "I need to go get my armor on" and rushes upstairs. Once in his room, he pulls out all the condiments, and starts layering the inside of jacket, then gets the armor. He goes back downstairs, and begins telling Papyrus all about his plan.

~Later that day~

SLASHHHHHHH*. His armor already destroyed, there is nothing else to take the hit. Sans takes a knee, and vanishes on the spot

(Sorry this one is short guys)


	5. A change of View

~I'm thinking of putting Sans and SwapUndyne together for this fic. comment your thoughts on that~

~Chara P.O.V.. Earlier that day~

SLASHHHHHH* Chara watched as their wooden knife sliced through his Jacket. Sighing, he took a knee. They watched as blood flew from the wound, and he slowly disappeared.

~Even earlier that day. Still Chara~

Chara approached him slowly. They weren't stupid. They knew something was wrong with Sans. They took caution as they approached him. As usual Sans stood there, but didn't deliver his normal speech about how they were good, and could still be saved. about how much he _believed_ in them. Instead, he stood there watching them.

They got closer, and he spoke "I see your face. You're wondering why i'm not spieling out praise about how good you are, and how much i _believe_ in you. It makes me sick". Chara was taken back. Even his voice was different. and he really didnt believe in them anymore? Chara didnt know what to think. "I'm not stupid you know" He says "I know you're here to kill me. but this time, i don't think its worth the risk." They chuckled. "oh you think that's funny do ya?" Sans took a battle stance, and initiated the fight.

Chara had first turn, and swung the knife. but Sans _dodged_ the attack. Chara was astonished. Since when could Sans dodge? They concluded that Papyrus must've been training Sans for this fight. Sans reached out with his hand, and Chara felt a heavy weight on their body. Then they were thrown, and landed on the ground. _hard_. They tried to get up, but before they could move, an array of bones flew out of the ground like spikes, and Chara had to reset.

After several iterations, they finally managed to destroy his armor, but then died. when they reset, he had his armor back on. Chara sighed, it was gonna be a long day.

Finally, finally!, after 237 resets,237 _fucking_ resets, they got him. They finally got him! he knelt down, and turned to dust.

~What really happened. Sans pov~

Sans felt the ketchup packets burst, and let them run down his jacket, before giving the signal to Papyrus, who turned on the leaf blower, sending snow everywhere. While he was hidden, he pulled out the container of parmesan, and dumped it all onto the ground, and mixed it with the snow, so it would lose its cheesy texture. As soon as he was done he dashed into the trees. he watched as the kid inspected the fake dust, as they nodded their head, and moved on.

~Thats all for now folks!~


End file.
